1. Field of the Invention
This invention relates to a measuring method for measuring the light emission from a pulse-excited sample so as to obtain a time resolved emission spectrum or a time resolved excitation spectrum. The time resolved emission spectrum is given by the three-dimensional curve including the time axis of the emission spectrum with the time t as the X-axis, wavelength .lambda. as the Y-axis, and emission intensity as the Z-axis. The spectrum represented two-dimensionally, is the emission spectrum at the cut face of the three-dimensional curve when cut by a plane perpendicular to the X-axis; in brief, the time resolved emission spectrum is the characteristic curve of wavelength-to-emission intensity at a certain time. The time resolved excitation spectrum is the characteristic curve of excitation wavelength dependency for the emission intensity.
2. Description of the Prior Art
The conventional measuring method for the time resolved emission spectrum or the time resolved excitation spectrum, is basically a certain sampling measurement which uses the time correlation photon counting method using a time-to-amplitude converter (to be hereinafter called a TAC), and has the highest sensitivity and accuracy. FIG. 1 illustrates an apparatus used to measure the time resolved emission spectrum. In FIG. 1, element 1 is a TAC and element 2 is a sample; element 3 is a pulse light source for pulse-exciting the sample 2; 4 is a spectroscope; element 5 is a detector, for example, photomultiplier, for detecting only the wavelength selected by the spectroscope 4 from among the light emission wavelengths from the sample 2; element 6 is a photomultiplier for detecting the light emission from the pulse light source 3; elements 7 and 8 are pulse shaper circuits; element 9 is a single channel pulse height and analyzer; element 10 is a multichannel scaler; element 11 is a stepping motor drive unit for adjusting the wavelength of spectroscope 4; element 12 is a clock pulse generator; element F is a filter and L is a lens.
The TAC 1 uses, as the start pulse, the detection signal from the photomultipler 6 which detects the light from the pulse light source 3 and uses, as the stop pulse, the detection signal from the photomultiplier 5 which detects the light emission from the sample 2. Accordingly, an output of the TAC 1 develops a voltage proportional to the time from the start pulse to the stop pulse (to be hereinafter called the reference time). The voltage is fed to the single channel pulse height analyzer 9 (to be hereinafter called an SCA). The SCA 9 is a linear logic converter having two pulse height discriminators capable of separately setting the pulse height discrimination level so that a logic output pulse is generated only when the pulse height of linear input pulses exists between upper and lower limit levels. In other words, the voltage crest values at the upper and lower limits of the SCA are properly adjusted, whereby the signal developed in a certain time region (the time window) of the TAC 1 is the logic output pulse of the SCA 9. Hence, the wavelength of spectroscope 4 is adjusted in the direction of fixing the time region. The aforesaid measurement is carried out at every optimum wavelength, and the output of the SCA 9 is input into channels corresponding to the respective wavelengths of multichannel scaler 10, thereby making it possible to obtain the time resolved emission spectrum in a certain time region of emission transient waveforms corresponding to the voltage window fixed by the SCA 9. Next, the time window of the TAC 1, as set by the SCA 9, is changed by a proper amount from the former time window and the spectroscope 4 is rescanned, thereby obtaining the time resolved emission spectrum at the different time regions, such operation being carried out by changing various time windows to repeat the same measurements as the above.
The above conventional method, however, has the following defects:
.circle.1 The spectroscope is scanned once to obtain only the emission spectrum at the time window of width .DELTA.t delayed by a predetermined time ti from the reference time, so that the information occurring at a time other than during the time window, in spite of being measured by the TAC 1, is not taken as the SCA 9 output and not used as data. Therefore, it takes a long time to obtain the time resolved emission spectrum because the time window should be shifted to various positions and the spectroscope should be scanned several times to repeat the measurement. .circle.2 In order to obtain the proper time resolved emission spectrum, the time region set by the time window decided by the initial and last time windows, the width of the time window, the intervals between the time windows, and the number of windows, should be properly selected, which is not determinable unless trial-and-error measurements are repeated several times, thereby requiring a great deal of time and labor.
The defects noted in the items .circle.1 and .circle.2 are involved in the measuring method for the time resolved excitation spectrum and the time resolved emission spectrum, because when the spectroscope 4 is disposed for the first time between the specimen 2 and the light source 3, the time resolved excitation spectrum is measurable in the same fashion as the time resolve emission spectrum.